Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface; and,

FIG. 2 is a front view thereof, shown in the context of different environment.

The dotted lines are for illustrative purposes only and do not constitute any part of the claims designed. 

The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 